The present invention relates to an antibody having a T-cell receptor specificity and higher affinity, conjugates of same with identifiable and/or therapeutic moieties, method of making the antibody and the conjugates, polynucleotides encoding the antibody and conjugates and methods of using the conjugates in the detection and treatment of cancer, viral infection and autoimmune disease.
The expression of specific peptides in complex with major histocompatibility complex (MHC) class I molecules on cells was shown to be associated with cancer and autoimmune disorders (1–3) and viral infections. In cancer, the discovery of these peptides emerged from the now well-established observation that human tumor cells often express antigens that are recognized by cytotoxic T lymphocytes (CTLs) derived from patients (1–5).
Moreover, it has been demonstrated that the immune response against the tumor is insufficient to cause tumor regression and that tumor cells can develop effective mechanisms to escape such an immune attack (6–9). Therefore, numerous approaches are being developed in the field of tumor vaccination in an attempt to augment the antitumor immune responses, including cancer peptide vaccines, autologous cancer vaccines, and the cancer-dendritic cell hybrid vaccine (7, 10, 11).
Because the specificity of the immune response is regulated and dictated by these class I MHC-peptide complexes, it should be possible to use these very specific and unique molecular cell-surface markers as targets to eliminate the cancer cells, while sparing the normal cells. A similar approach can be undertaken to eradicate viral infected cells and cells presenting targets for autoimmune attack. Thus, it would be very desirable to devise new molecules in a soluble form that will mimic the fine, unique specificity of the T-cell antigen receptor (TCR) to the cancer/viral/autoimmune-associated MHC-peptide complexes.
One promising approach is to generate recombinant antibodies that will bind the MHC-peptide complex expressed on the cancer cells surface with the same specificity as the TCR. These unique antibodies can subsequently be armed with an effector cytotoxic moiety such as a radioisotope, a cytotoxic drug, or a toxin. For example, antibodies that target cancer cells were genetically fused to powerful toxins originating from both plants and bacteria, thus generating molecules termed recombinant immunotoxins (12).
Antibodies with the MHC-restricted specificity of T cells are rare and have been difficult to generate by conventional hybridoma techniques because B cells are not educated to be self-MHC-restricted (13–16). The advantages of antibody phage-displayed technology makes it possible to also select large antibody repertoires for unique and rare antibodies against very defined epitopes. This has be demonstrated by the ability to isolate by phage display a TCR-like restricted antibody to a murine class I MHC H-2Kk complexed with a viral epitope (17). Evidently, this antibody, being directed at mouse MHC, is useless in the treatment and diagnosis of humans. So far, attempts made by the same group to develop a TCR-like restricted antibody to a human class I MHC have failed. More recently an antibody was isolated reactive with the melanoma antigen MAGE-A1 in a complex with HLA-A1; however this antibody exhibited a low affinity and could be used to detect the specific complexes on the surface of antigen-presenting cells only when expressed in a multimeric form on a phage and not as a soluble antibody (18).
There is thus a widely recognized need for, and it would be highly advantageous to have, a TCR-like restricted antibody to a human class I MHC devoid of the above limitations.